A problem in the separation of the fluid in the liquid state is that the proportion of the second liquid in the first liquid after separation in the centrifugal separator can be too large. As a result the product after separation is not sufficiently pure.
WO 2004/039922 discloses to a device for cleaning of lubricating oils. The lubricating oil is separated in two stages, in which it first passes through a centrifugal separator and then passes further downwards through an outlet directly into a vacuum-chamber. The second separation stage takes place in the vacuum chamber. A vacuum pump is arranged in the connection to the vacuum chamber and functions in a way such that it lowers the pressure and takes away water which usually condenses from steam from the vacuum chamber, which makes the device complicated and expensive.
The fluid that is to be cleaned can, as shown in WO 2004/039922, consist of a lubricating oil that contains mostly water as contaminant and does not contain volatile components. Use of a vacuum chamber after the centrifugal separator for taking away the water can function satisfactorily in this case. If, however, a fluid is to be cleansed from, among other things, water that additionally contains a proportion of volatile components, separation in the vacuum chamber does not work. This is because evaporation is excessive, since the volatile components evaporate more easily than the water, i.e. at lower temperature and/or higher pressure, with the result that an unnecessarily large proportion of volatile hydrocarbons escapes.